You're looking at it in terms of scoring the entire fight. Break it down and it makes more sense.
Rd 1: Tannen does little to nothing in the stand up, lands a total of 3 strikes in the clinch (and I'm questioning how hard the strikes were seeing one shoulder strike "didn't do any damage"), was taken down twice, and had the clinch broken twice. I give Alderson a 10-9 round.
Rd 2: Tannen lands only 5 punches in the clinch, gets taken down twice, is controlled on the ground, and is arguably controlled in the clinch as well as Alderson breaks the clinch twice and initiates his own clinch once. I give another 10-9 rd to Alderson.
Rd 3: Round 3 is dominated by Alderson. He takes Tannen down early, controls for a minute or two until the ref sees enough and stand them up. He then fails with a couple of attempts, lands a nice leg kick, and takes Tannen down again. Alderson controls for another minute or two until the second ref standup. Moments later, another takedown and it's over. I score another 10-9 rd for Alderson.
In total, 30-27 Alderson in a very boring fight. Alderson does his best Fitch impersonation and basically had the plan of taking Tannen down and controlling him. Boring (34% rating) but effective.