I am inclined to think Grewal's motivation for taping conversations with Murphy and Dosanjh is irrelevant.
Maybe Grewal did intend to cross the floor. If that is so, why didn't he? There is every indication that had he abstained in budget vote, that he would be on his way to Cabinet in the government -- because as Dosanjh said: 'Cabinet is easy'. So, if that was his desire, Cabinet within the government -- and Murphy obviously didn't say no -- in fact, he all but said yes -- then why didn't Grewal jump at the chance?
If we look at the situation in context, and remember what happened with Inky Mark, then maybe Grewal's assertions have more credibility.
Grewal says he was approached a few times, and declined. That would give him an opportunity to be prepared that it might happen again -- Murphy or Dosanjh might have said: 'don't say no just yet, we'll let you think on it'.
Given that Inky Mark publicized what he characterized as an approach by the Liberals for his vote, and that Inky Mark was swifty and summarily dismissed by both the Liberals and the media -- Grewal's decision to tape the conversations is more clear.
Had Grewal told anyone that the Libs were courting him, their response would be 'why would we want him -- he's (conveniently) under investigation for graft'. He would have been mocked and ridiculed in the same way Inky Mark was, and he would likely have been disbelieved.
However 'wrong' it might have been for Grewal to tape these conversations, the fact remains that there would have been no way to corroborate his accusations. It would have been the 'he said/he said' that the press is trying to make it now.
Rather than playing the 'they're both just as bad' game, the press and the public should demand more from government representatives like Murphy and Dosanjh. They are in positions of power and influence and their abuse of public trust is clear. Grewal getting it on tape, didn't make it so.