Likely a direct feed but the books may not send on the same intervals.
For example on Xavier/Butler game today.
Here is BOL's line history. Only 2 Updates since 11:30 this morning.
Here's
Bookmaker's line history. 5 updates since 11:30 this morning.
This seems to indicate the sportsbooks "sends out" updates and BMR picks them up... BMR is not going out to pull the lines from the sportsbooks (either that or the lines at BOL aren' moving much - not likely).
The pace of sportsbooks sending out updates probably varies by how much action is going on that day and I bet all delay the updates slightly.