JL may have just been using that term loosely in his tweet or for restriction of characters in a tweet. I've read several reports just now and none say it was a breach.
From what I'm reading, it was an if / or requirement. If the Dome is top tier, the Rams are obligated to stay or if not, than they can choose to shift to a year to year or leave. Thus far, they have chosen to shift to a year to year as provided in the lease.
"The St. Louis Convention and Visitors Committee confirmed Monday that the
Rams informed the group of its intentions to shift to a year-to-year lease agreement for the Edward Jones Dome,
according to the Associated Press.
The CVC operates the dome. The Rams had a Wednesday deadline in order to notify the CVC of such a shift, a change it is permitted to make should the stadium be deemed not among the top 25 percent best in the NFL based on certain criteria."
If I'm correct that this was an "if or" type of provision, it wasn't a breach. A breach is not fulfilling an absolute requirement of the lease. This doesn't sound like an absolute requirement but an option for the dome Rams.