Looks like they're attempting to use the Level 4 Travel Restriction, however, it does say (my highlight in RED:
"There is no cover under any section of a policy if you remain in a region or country for which the DFAT advisory rose to Level 4 (Do Not Travel) while you were there, if you were able to leave but instead opted to remain."
I have friends who are working in coughet right now, and their insurer originally stated (on Monday 16/3) they would be covered for "emergency accommodation" which included Covid-19 lockdown. When I advised their PA to check this again on Wednesday, after the announcement that our borders would be closed to all foreign nationals, the insurer declared that they would not be covered, as Covid-19 is not "terrorism or a natural disaster". They have ultimately been forced to return to AU, not because of the TH government or our border closures, but instead, due to SQ cancelling flights; they got the last 3 seats for their flight back to ADL on Sunday 22/3.
In essence: it appears that if you have to stay due to local country laws, they will cover you, but if you choose to stay under the current Level 4 alert (and aren't in lockdown), you're on your own. Doesn't help if you're involved in a car accident on the way to your flight which lands you with a medical bill, after all, you're attempting to leave and get hurt/lose luggage/or are delayed, it's not through any fault of your own.
Of course, they could use the fact that on 31st January 2020, the WHO deemed this event an international health emergency, as yet another way to wriggle out of payments. Overseas prior to this announcement, the policy may cover you, but who knows - I'd be contacting them to clarify such a scenario as described above.
Good luck!