It's very feasible they offered Jaylen. The Boston Globe ran a story saying that Celtics president of basketball operations Brad Stevens and coach Ime Udoka have also been in constant communication with Brown, who understands the situation according to Boston Globe's Himmelsbach. That certainly doesn't sound like he was never offered. Since then they have had multiple opportunities to deny the reports and have not.
Also, sounds like it's a potential money issue for Boston as well and in recent years have tried to avoid the luxury tax. Sounds like they are willing in the short term to go for it but doesn't sound like they want to be in the luxury tax long term. Brown is eligible for an extension this year and some feel Brown won't resign without getting the money he wants. He is looking for three-year, $111 million contract extension. Plus, if he makes any All-NBA teams over the next two seasons he is eligible for a five-year, $273 million contract with the Celtics when he becomes a free agent in 2024.