If they have worked there for nearly a year, I would hope that they would have more than 2 weeks vacation time accrued? I am guessing there was also some more vacation time that needed to be paid out?
Secondly, you said your friend quit 2 months after taking their vacation, but the CEO's email says "take 2 weeks vacation then give notice the next week". Did you friend actually give notice to quit a week after vacation (i.e. give them about 6 weeks+ notice that they were leaving) or serve notice 2 months after returning from holiday?
Having been a business owner who has hired staff in the past, yeah it sucks when employees quite while on holidays - mainly because it gave me no time to plan to hire a replacement, or to have them help train/handover to the replacement staff member.
But if they have taken holidays that were legally owed to them then there is nothing I can do about that, and it would be unprofessional to vent about it as it is well within their rights (albeit inconvenient to the business).
It also comes down to whether the employer lets their employees take their leave in advance (e.g. your policy is 4 weeks holiday per year, and a staff member wants to take the entire 4 weeks when only 6 months into their employment). Some companies let you do that, sure - but in THOSE cases, if the employee quit while on holiday then there is a real issue because the took an extra 2 weeks holiday that they hadn't yet fully accrued. Though in your friends case, unless they had taken other leave earlier in the year, they may still be within their accrued allowance?