As Dan Bron's comment points to, the basic definition of "getting on one's high horse" is:
Behaving arrogantly and pompously
However, sometimes understanding meaning does not necessarily translate into wise or effective usage, and the example deserves some explanation.
In fact, the instance quoted in the question (from http://openmymind.net/2012/5/30/Client-Side-vs-Server-Side-Rendering/) should not be taken as the most common application, for two reasons:
1) we most commonly see this expression phrased as to get on one's high horse, not "get on a high horse"
2) almost all of the instances of this idiom that you will find (in speech and writing) come in critical reference to the behavior, attitude, assertions, soap-boxisms, etc. of another person, as opposed to oneself
In the quotation in question, it is used (atypically) to preempt accusations of arrogance or pedantry.