The weather was okay at the time. Lake Travis is a fairly large lake so normal waves can be difficult. The real problem comes from houseboats which create a huge swell, that is slow moving and deceptive. You don’t always see them coming and if a small boat hits one at the wrong angle it can be really bad. With so many boats in such a small area and house boats mixed in, it is possible that the swells were running all over at every angle. Even if you have operated a boat all your life, you can still be caught off guard if you haven’t experienced it before.
Yes, it’s likely “harmonic” jumbo swells caught several skippers unawares.
We used to swing the tubers into them. Kowabunga! (We were early years tubers, used semi truck tubes with a ski handle wrapped and duct taped to it. Still had ski belts then.)