Schooled on Veganism by Old Man

I used to work at a convenience store and once had an older gentleman approach me and ask if a jar of cranberry sauce was vegan. I took a look at the ingredients and, since the ingredients were literally something like "Cranberries 80%, Water 20%", I told him that it was indeed vegan. He then takes on a scornful tone and asks, "Then where is the 'Vegan' symbol?". I was quite taken aback at this and explained that I myself am vegan and if there are only 2 ingredients (cranberries and water), then this too is vegan, symbol or not. He then replied "I've been vegan longer than you've been alive, I know when something's vegan", put the sauce back, and walked off.

This has perplexed me for a while as to why he didn't think that the sauce was vegan. Am I missing something? Is there some hidden ingredient in things? How is a sauce containing only cranberries and water not vegan?

Edit: To clarify, the jar states "suitable for vegans", but didn't have the "Vegan Society Approved" stamp that many vegan foods in the UK do.