I've read the signs, and the websites, and know people who have unfortunately been in abusive relationships and I still disagree that you can simply suggest that this is an abusive relationship on the basis of 4 disagreements from a sample total of 1700.
I think it has to be taken more on the basis of the length of the relationship rather than the number of text messages, which can run into thousands simply because they can be one word, one smiley, a few xxxx's, back and forth .. I can clock up hundreds of those sorts of messages on another forum I belong to, plus also when I used to MSN message with my abusive ex partner, we could clock up hundreds of them, just in one night (and Whats App is only a mobile phone version of MSN messenger, basically). So, quite honestly, I wouldn't put too much faith in the fact that there were 1000's of 'normal' messages because that's fairly easily done, and is quite the norm these days .. it doesn't really have a great deal to do with whether a relationship is normal or not.
They had actually only been dating for 3 months, and to me, that is what is more relevant .. the fact that there were four extremely concerning exchanges during the third month (i.e. they had only been dating around two months by then), and they are not the type of message you would expect to see between a couple during the first flush of love, and they are not just arguments about normal stuff, these are much deeper disagreements which relate to OP being controlling and possessive. Also, as said, much of the stuff would've been carried out face to face .. don't forget, these phone messages actually relate to things that have actually taken place at a previous point in time, and something which has prompted the text arguments .. so, not only do you have the text disagreement but you have the actual occasion (for instance, the engagement party) itself where things weren't going quite so swimmingly. Those text messages cannot just be taken in isolation, but they were a really big indicator as to what was going on/going wrong with that relationship .. a massive indicator, in fact.