Title text: Although the Markov chain-style text model is still rudimentary; it recently gave me "Massachusetts Institute of America". Although I have to admit it sounds prestigious.
Swiftkey is a product that is installable only on Android-based phones and tablets. Swiftkey have noticed their inclusion in xkcd and have created a blog post for other users to comment with their default phrase when they hit the "central prediction key". The results are pretty funny. 
The statement “I am so sorry - that's never happened before” appears to be a sexual reference, something that a guy might say after a particularly unsatisfying sexual encounter in an attempt to convince his sexual partner to give sleeping with him another try some time, even though they didn’t like it that time. Since this is apparently Cueball's typical sentence, he presumably has texted that phrase many times before.
In the title text, a Markov chain refers to a system that transitions between a countable number of states, based only on the current state and none of the previous ones that led up to it. Swiftkey follows this property since it provides outputs based only on the most recently entered word or words, not the whole sentence.
"Massachusetts Institute of America" is a nonexistent organization. The name appears to have formed by combining "Massachusetts Institute of Technology" and either "[Field] Institute of America" (e.g. Mining) or "United States of America". This illustrates the memoryless property of a Markov chain; after generating "Masschusetts Institute of", Swiftkey may have attempted to predict the next word using only the last "of" or "Institute of". Since it was not considering the word "Masschusetts" at all, the word "America" was viewed as the most likely follow-up.
- [Cueball shows off phone to Megan.]
- Cueball: Have you tried SwiftKey? It's got the first decent language model I've seen. It learns from your SMS/Email archives what words you use together most often.
- Cueball: Spacebar inserts its best guess. So if I type "The Empi" and hit space three times, it types "The Empire Strikes Back".
- Megan: What if you mash space in a blank message?
- Cueball: I guess it fills in your most likely first word, then the word that usually follows it...
- Megan: So it builds up your "typical" sentence. Cool! Let's see yours!
- Cueball: Uh—
- SwiftKey: I
- SwiftKey: Am
- SwiftKey: So
- SwiftKey: Sorry—
- SwiftKey: That's
- SwiftKey: Never
- SwiftKey: Happened
- SwiftKey: Before.