I'm surprised this isn't more discussed in the comments. It's a major element to consider when you're selling your business. He correctly identified it after all, as a potential deal breaker.
You're selling something, so in an acquisition you will have to represent and warranty what you actually own and you're selling. This sounds simple on its face, but technology isn't nearly so well-defined and legally sorted as, for example real estate.
In software, even if you are 100% certain you can transfer all of the code and there are no potential content copyright issues or latent prior agreements by yourself or other sellers, current/former employees who think they own something, etc, you still have at a minimum, a hard-to-quantify "Sword of Damocles" in the form of thousands of potential patent claims hanging over you, trolls or not, it doesn't matter in a sale. As in business itself, the bigger the money involved, the more visible you become to potential claims.
A publicly-traded buyer is likely to be less flexible on terms, but in any case you as a seller have also to consider that in a sale, you're most likely going to be forced to shift liability from your corporation to yourself personally. If you're prudent, as this seller was, you realize this creates a time period increased personal risk, despite your increased assets. Keeping this period as short as possible and limiting its scope and magnitude is your objective.
A few limitations I can vouch for making it past public company scrutinity are 1. any dispute costing less than $X are not your responsibility. 2. a maximum liability limitation equal to the purchase price in cash / shares (in case share prices drops) 3. a time limit of two years or less. 4. escrow of a portion of the purchase consideration (shares and/or cash) as a warranty cap for the duration of the warranty, perhaps with release/reduction over time. The tax treatment of this arrangement would have to be considered carefully.
Finally, it's worth noting that insurance for an acquisition deal may be available from big name insurers, likely for some low single-digit percentage of the deal value. However, their legal department will undoubtedly be more sophisticated in this area than your counsel, so at its worst insurance gives you little more than a contract with an insurance company over which to sue, likely at great cost.
Overall, as lawyers always say, "it depends." Unless the deal and/or your resources are immense, likely it is a problem with no risk-free solution. If you're young and have nothing to lose, risk is an easier choice. For everyone else, all you can do is optimize based on present knowledge.