I think timing is crucial though
May 2020 we were still deeply in the throes of the first lockdown
December 2020 we were hurtling full throttle into the second full lockdown
May 2021 we were rapidly coming out and heading towards Step 3
It was a crucial byelection (which spoiler alert they lost) and were probably desperately trying to avoid. As Party Leader he probably did need to be there.
Plus it looks like a diet coke to me which would make sense?
But crucially does it actually matter. Even if he had done the same as Boris Johnson and Downing Street they are still guilty and are the Government in charge. Who should be leading by example which they were not