I can't see them doing a 16" launch without some type of event. Apple usually likes to tout major launches like this would be to show off new features.
The current versions of the MacBook Pro were all released without events (the high-end in May, the low-end in July) including significant new features like 8-core options at the high end and touch bar* in the low-end. Likewise, the iMac in March.
* NB: Note the careful choice of words:
significant new features...
Some versions of the rumour suggested that the 16" would even have the same CPU/GPU options as the current 15" - and 16" isn't going to be night-and-day better than 15.4". The design in the leaked icons is essentially the same as the current range, just very slightly bigger and with slightly thinner (but nothing special c.f. competing PCs) bezels.
The reality is that this is the most
boring update to the MacBook range in a while - which isn't necessarily a bad thing. The most hotly debated improvements represent Apple
backtracking on things like the escape key (confirmed) scissor keyboard (highly likely) and, speculatively, restoring legacy ports (not holding my breath & 3 years too late) or better cooling/larger battery due to the larger size.
So, no, I wouldn't find it surprising for this to be snuck out without a launch.
...that's not to say that a 2020 launch, poss. along with new processors and matching revisions of the 13" MBP isn't
more plausible, but we had a glut of rumours (along with the 'leaked' icons) suggesting it was imminent.
Other bits of idle speculation:
(a) It was a contingency plan in case the latest tweak to the butterfly keyboard didn't stem the reliability problems, but they did, so now its been delayed.
(b) It was planned for an October launch event but cancelled because of production problems/Intel CPU supply problems/exploding batteries/global escape key famine/entire production run eaten by a giant mutant space goat/Magic 8-ball says "Outlook not so good." etc.