I would start by saying that your professor has only a marginal a point at best, and what he did was really kind of a... well, it wasn't very nice.
My number one rule before I get into any meeting is to know who my audience, and that goes doubly for presentations. While it's true that there may be one or two attendees at meetings that you don't anticipate, your presentation should be tailored to your audience. In any given job, you're going to know pretty much who this entails, and what their agenda might be, ahead of time.
My worst presentation story actually comes from when I was applying to work for the Denver Broncos as a journalist on their team website. For a while I had been running my own Denver sports news site as more of a practice writing sports stories than anything else. As I had neither a press pass nor the availability, I borrowed quotes from different sites that I assumed were from public news conferences and used them in my stories. I was still young and stupid, however, and I didn't attribute the quotes to the proper sources. I didn't think that would be a problem, as next to no one ready my site at the time (we had a daily user count in the low hundreds) and I didn't submit any of those stories as part of my portfolio.
When I went for the interview that day, I thought I'd be meeting with one of the DenverBroncos.com editors in his office at Mile High. As it turned out, I was meeting with both site editors, the head of the marketing department, and the head of the communications department, in one of the stadium luxury boxes. This was very off-putting, but I did my best to take things in stride. We got to talking about the Broncos, my career path, and why I wanted to work for the team.
Eventually, one of the editors pulled up my website, and one of the stories I had written early on in the site's creation. He pointed out that not only did the story have an unattributed quote that came directly from a story he wrote for DenverBroncos.com, but it also had a picture from the site as well. He asked me why I thought either was appropriate, and what had been to that point a fairly upbeat atmosphere fell dead silent.
I decided that honesty was the best policy. I explained that I used the site as practice for my writing more than anything else, that I assumed (wrongly) that the quote came from a publicly-broadcast press conference, and that I was a lowly college kid with no budget to properly purchase rights to pictures. I admitted that it was poor judgement, outlined the rules of journalism as I knew they applied to the situation, apologized, and vowed to remove the content if they preferred.
After my answer the interviewer in question softened a bit and said I could keep everything up, but asked if I could see why that situation was concerning to them. Things never really recovered after that, and things remained more subdued than before.
When I left the interview, I was absolutely crushed. I grew up in Denver as a Broncos fan, and getting this job would have been a dream come true. I remained hopeful, but not optimistic. When the days faded into weeks and eventually into months, and still no call had come from the team, I assumed that I had been passed over.
I was on my way to my job at Sears as a Lawn & Garden salesman when I finally got the call from the head of the marketing department. I pulled into a parking lot on the side of the road and got out of the car as we exchanged pleasantries at the beginning of the conversation, although I expected the worst. It was a good thing I was already out of the car, however, because I don't think I've ever jumped higher in my life than when I was offered the position. To this day, it ranks as the third happiest day of my life, behind only asking my wife to marry me, and our actual wedding day.
So what's the moral to this story? I'd say it's to know your audience as much as you can going into a meeting, be prepared to think on your feet and give your honest opinion and/or explanation, and to never assume that a presentation went as bad as you thought it did. Apart from these three basic principles, I'm not sure there's more you can do for any general preparation that will leave you better-suited to deal with any eventuality that may arise.
It certainly worked well for me.