To me it actually seems more likely that the leak came from the team side. The numbers that leaked benefit the front office and make Vlad look greedy and unreasonable. If Vlad was the one who leaked it, he might just be a really dumb guy.
One part from Shi's article stood out to me.
https://www.sportsnet.ca/mlb/article/blue-jays-and-vladimir-guerrero-jr-hit-deadlock-over-50m-gap/
Both possible motives seem to benefit the front office. If it was to try and push the sides toward common ground, it seems like the front office may have leaked it because Vlad was telling the media their offer wasn't close, and they wanted to fact check him plus try to move talks closer to a deal.
Vlad is the one who seems incentivized to just let things play out, and he doesn't seem like he wants to push sides toward common ground, instead he seems excited about the possibility of betting on himself and testing free agency.
If it was to try and turn opinion against one another, then that worked out for them too. How would this leak have had the opposite effect? I don't even think it's possible that this leak could have turned opinions in favour of Vlad, once you see the offer details. Again, if Vlad was the one who leaked it, he might just be a really dumb guy.