Yea. The incoming jet was on a 5-mile final. Being a small jet it's "slow" so that 5-mile final is 3-5 minutes. You can see 19:04Z when the Southwest jet get's the "line up and wait". 19:07Z is the missed approach. If ATC has given them the departure clearance relatively quickly, there would have been no issue as Southwest would have hit the gas and been long gone... but ATC didn't.
This is not uncommon for aircraft to get on the runway and take off while another aircraft is on final. If you want a good video of how this more typically works (and sometimes doesn't work), here's one from an incident at SFO about 2 months ago: https://www.youtube.com/watch?v=DrRGde5J8mo
In both the SFO cases, they got the "go around" from ATC much earlier and no one got too close to each other. Keeping in mind that SFO is extremely busy and lands two parallel runways at the same time: https://www.youtube.com/watch?v=YsKhZm78DuY
This is not uncommon for aircraft to get on the runway and take off while another aircraft is on final. If you want a good video of how this more typically works (and sometimes doesn't work), here's one from an incident at SFO about 2 months ago: https://www.youtube.com/watch?v=DrRGde5J8mo
And another from SFO: https://www.youtube.com/watch?v=E4cewwhcL5c
In both the SFO cases, they got the "go around" from ATC much earlier and no one got too close to each other. Keeping in mind that SFO is extremely busy and lands two parallel runways at the same time: https://www.youtube.com/watch?v=YsKhZm78DuY