Running multiple official MLB team accounts is hard work. It's a lot of passwords and usernames to remember. Ask whoever runs the Blue Jays' Twitter, because they also run that of the Texas Rangers.
Three minutes later, the exact same tweet showed up on the Rangers' feed, but as you can already tell, not before people discovered the mistake made on Toronto's:
There isn't just one person running all 30 accounts, as most teams have their own social media people. There are plenty out there who get part-time help from MLB, though, and it's kind of amazing mistakes like these don't happen more often.