What does this number mean in PGA Tournament scores?

Golf newbie here. I’m watching the Valero Texas Open, round 4. It just started, and a player just completed the 1st hole making a Par in this Par-4 hole (thus having made 4 shots so far).

However the scoreboard says he’s got a "1" out of 72. What does this "1" mean? Shouldn’t it say he’s got "4" (as in 4 shots so far)?

I remember round 3 yesterday they all ended with scores of around 65 or so out of the 72 shots total. But also I remember some of them being at the 18th hole with a score of just "17", which was suddenly updated to "65" when the round ended. Is this a delay thing? Does this number mean a different thing? Thanks!