There is quite a well developed polling industry in Ireland with a generally good reputation for accurate results.  There is little reason to think the Commission would want to skew the results - which are in any case unflattering for them.  I presume the research brief was to allow respondents to volunteer their reasons, and failing that to offer some options - perhaps with a bias to getting some actionable data - i.e. stuff the political system can actually address - not  "my mammy voted no so I did..." etc.

However until the full survey report is published we can only surmise.

"It's a mystery to me - the game commences, For the usual fee - plus expenses, Confidential information - it's in my diary..."