They probably decided they wanted to be part of that future market about AI and therefore want to invest in AI/ML startups. Someone sold your company internally as being a nice fit for the AI portfolio, but when you answered the question about ML with "No" the door was shut.
From someone who makes large trade deals as his daily business, I learned "Never say 'No'" (during a negotiation). In most cases, it is better to be diplomatic. So might have been better off with something like:
'So far we had decent results without ML, but we are constantly evaluating options to improve our technology, which includes optimizations based on machine learning.'
That way, some might hear '[...] includes optimizations based on machine learning.', while you just said 'we do not use machine learning' ;-)