Don't use Summer and Winter for event invites, it's "northern" and not inclusive
nature.com
nature.com
This is like saying “Stop inviting me to uninclusive birthday parties, it’s not my birthday.”
Worse, if you're in the tropics, northern hemisphere or not, there are only two seasons, so these seasonal references make even less sense.
If it is truly a global, virtual event not linked to any one place (or a group of physical events), then yeah you shouldn't use either.
In other words, if you feel you need to question whether you're invited when someone invites you to his winter conference because it happens to be summer where you are when the conference takes place, by all means consider yourself to be disinvited. It is clear the seasonal discrepancy is too much hardship for you and it is also clear the conference is much better off without having to cater to yet another victimhood hierarchy. Just ignore the invitation and be done with it.
For those who nevertheless want to consider going to a winter conference it is probably more informative to know it is going to be bloody cold - i.e. winter - when that conference takes place. This is good to know if you come from the southern hemisphere where it can be bloody warm around that time.
We should immediately classify all human knowledge by the geography of its originators and refuse to accept anything not of "southern" origin until the imbalance is addressed.
Remember, only statistics can enforce equality!
There's a utility to telling people early in the planning stage "Hey, we're gonna be hosting this thing vaguely in summer" and send out the proper date when you've set one.
(Though point taken about the seasons, maybe something like "2nd Quarter" would be less culturally ambiguous?)
They have not provided examples; for all it seems, their suggestion could attack the use of "we do it twice per year, so we called one the Summer event and the other the Winter event". Which is just a fuzzy adoption of the terms for practical reasons. Not an «oversight», not a «mistake»: just a quick neutral labelling for calling things some way.