Sounds like a suspect claim here - they are obviously investigating everything very carefully. A lot of scams going on at the moment. Especially those businesses which are for sale - and suffering mysterious fires!
Bangkok Bank provide foreigners with what they call a savings account which you can take money out whenever you want - but for immigration purposes the important thing is that the account should be in the applicants name only.
Maybe he is getting confused with the 40,000 bht a month proof of income, if he does not have 400K in the bank. They would then need to see 12 months statements.
They have had a lot of problems with keeping up to date with hotels that have closed due to Covid. I booked a hotel in Chiang mai about a month ago. Paid by credit card, had the voucher issued and when I got there the hotel was closed up with a notice pasted on the door saying it would open again next month! Luckily it was a simple matter to walk around the corner and book into another hotel. However just imagine if it had happened to a couple of weary travelers coming on holiday from another country.