My mistake. I should have googled it first for sure. Sounds like a call in the WSOP rulebook to me since he used all the same denomination.
Originally Posted by WSOP rules
92. Oversized Chip Betting: Putting a single oversized chip or multiple same-denomination chips into the pot will be considered a call if the Participant
doesn’t announce a raise. For example, pre-flop, blinds are 200-400: A raises to 1,200 total (an 800 raise), B puts out two 1,000 chips without
declaring raise. This is just a call because removing one 1,000 chip leaves less than the amount needed to call the 1,200 bet. To make a raise with
a single oversized chip, a verbal declaration must be made before the chip hits the table surface. If a Participant says "Raise" as an oversized chip
is placed into the pot (with the word Raise being announced prior to the chip landing on the table surface), but doesn’t state the amount, the raise
will be the maximum allowable up to the denomination of that chip. After the flop, an initial bet of a single oversized chip without comment will
signify a bet equal to the size of the chip.
For this case, amount needed to open is 1200, and 3 equal denomination chips (the minimum number needed) were used to satisfy that action, and nothing else was verbalized. This becomes a min-open with rule 92, imo.