It does sound a little weird at first, but I believe that is correct. The idea is that estimated payments normally due on 4/15 are supposed to be for income earned between 1/1 and 3/31 (mostly before the shutdown). People impacted financially by the virus presumably did earn normal income during most of that period and set estimated tax money aside, but now have no ongoing income and need that money to live on. Because of the virus, they are now permitted to delay the estimated payment until July.
The 6/15 payment is for income earned from 4/1 to 5/31. I think the idea is that if you had normal income during that period, you should have no problem making the usual payment. On the other hand, if you did not have normal income during that period, you would not owe much, if anything, in June.
Come June, you should take a close look at your situation and probably recalculate your estimated payments for the entire year. You may have slipped into a lower tax bracket.
