He may be senior, but he's not making sense. If somebody asks for your slides at your talk, there's a good chance they've seen the talk. So they have the context, they may just want a refresher later. Or maybe they saw something on a slide they couldn't make out before you advanced.

Besides, what do you care? What's the real reason you're refusing?

Here's the logical extension of the suggested alternative: don't bother to give a talk. Just send copies of your papers.

But that sounds silly to me. I think there's probably a reason people both give talks and write papers. So here's my suggestion: if your slides aren't worth giving out, don't show them when you speak.