I find it hard to believe you couldn't attend a conference and visit a couple of startups on a normal entry from the US, unless you are not a US citizen?
I've been to Vancouver many times as a tourist, a few times for conferences / standards meetings, no problem, no visa required.
Depends how you answered the questions and what type of border services agent you got.
A former employer of mine had U.S. based employees that were subject experts / trainers on proprietary systems - Written internally, used internally. We had to do training sessions via teleconference after the border services turned our trainer back. Our Legal followed up with border services and was given the requirement that we advertise nationally for someone to fill the training role for a period of i-can't-recall how many weeks then re-apply if not able to fill the role from a hardworking but unemployed fellow Canadian.
It was utter crap. Time we didn't have to look for a person who didn't ( couldn't ) exist seeing as it was a new system, written outside Canada. Trainers had crossed previously to fill similar roles without issue. go figure. We ended up doing it over the phone..
I've been to Vancouver many times as a tourist, a few times for conferences / standards meetings, no problem, no visa required.
This doesn't sound right.