The text on the Tesla website mentions https://globenewswire.com/

Anyone can setup a real time account for free.

Also the WSJ article pretty clearly used the press release as a source, so mentioning that is a separate issue from whether it is a good or bad source.

(unless you think the WSJ called Tesla and verified specific facts like "4,820 Model S and X vehicles were in transit" vs "The company said 4,820 vehicles were in transit at the end of the quarter")