I think the heated (or not) family meeting served as the trigger for something that had been contemplated for quite a while. So it didn't give anyone an idea; all it did was give the final push to making a previously entertained idea a reality.
I suspect that Bob probably did have a financial accountant or tax preparer. However, it's the old problem of GIGO: an accountant or tax preparer can only deal with the information that they have been given. If Bob didn't have the information as to what was going on, then anyone he used as a consultant probably didn't figure it out either.
As a purely made up example, say Jane Public's daughter Jennifer married a man named John Shady. To help Jennifer and John get a headstart towards being in a good position to start a family (Jane really really wants grandbabies to cuddle), Jane offers to fund a home for them. She offers them a mortgage based on the best terms commercially available at the time, not realising (or caring) that John Shady's credit score is horrible and there is no way he could qualify for those terms from a regular bank. She's not digging around into her son-in-law's credit score.
Jennifer and John take care of finding the house and negotiating with the homeowner, who is acting as his own realtor. They bring the final total to Jane, who doesn't realise it is for $25K more than the homeowner accepted. Jane has seen the price in the ad and the sum that Jennifer and John brought her is somewhat lower.
A financial advisor would be unlikely to catch this bit of fraud. It wouldn't take much digging to discover it but since Jane has no misgivings about the transaction and only purpose in consulting her accountant is to make sure it conforms to IRS rules (want to avoid that gift tax, you know), the consultant doesn't check to make sure that all the figures are on the up and up.
A forensic accountant would nail this one easily because their task is to dig out all the details regarding every transaction.