This. I’m willing to bet you could pull one of the wires out of its lug on the receptacle. The other possibility is that there was some insulation trapped between the lug and the wire. This is why I like the Tesla wall chargers. They have a thermal sensor that will shut down the charger and they flash a light pattern that lets you know what is wrong. Way too many electricians do not carry a torque driver to torque lugs to manufacturer spec.
I’ve seen this happen on a 400A panel. Neutral started to spark when under load because the lug was loose. It was…messy. You might want to have an electrician go through the rest of your distribution panel and your receptacles even if it’s just for your own peace of mind.
Glad to see it is only for busy sites. I live in Halifax, NS in Canada and have a 2019 Model 3 SR+ with over 130,000 kms on it. When I travel from Halifax to Moncton in winter weather the nav system usually tells me to charge to more than 90% in Enfield so I can make it to the Supercharger in Aulac, NB.
When traveling to Cape Breton, I usually charge to 100% in Enfield because everything North and east of Halifax is a bit of a DCFC wasteland. There are a few 50kw Flo chargers but they are single stations spaced around 100kms apart so they tend to be pretty busy.