Touchscreen activated by clothing?

The following Garmin Support articles linked below are recommended in relation to the concern you mentioned: 

• Preventing the Touchscreen of an Approach Watch From Changing Screens
• Types of Touchscreens Found On Garmin Outdoor Devices

Make sure to hit a ball when using the Tempo Training app to get the reading during the swing tempo session. 

Also on your watch open Settings > User Profile > Ensure the wrist is set correctly for the wrist you are wearing the watch on. 

To ensure proper shot detection from the watch, make sure to wear the watch on your lead wrist (left wrist if using right-handed clubs, or right wrist if using left-handed clubs). 

The watch should be attached securely resting on the top side of your wrist and not on the underside in order for shots to be detected properly during golf rounds or when using Tempo Training. 

I have confirmed by testing on the s70 the concern you mentioned on my end, that locking the screen does not affect shots from recording. If you continue having concerns after following all of my suggestions above, please let me know, as I would like to gather more info from you on the issue. 

The Tempo Training feature will work as designed if the suggestions in my previous comment are followed when using the app. 

The lock screen option can be used during the Tempo Training if you are needing to lock the buttons while using the Tempo Training app on the watch. 

Please note the section regarding the requirement of the club needing to hit a golf ball when swinging the club if you are using the Tempo Training app. If a ball is not hit, the watch is not designed to pick up the swing. The golf ball is needed in order for the watch to provide the tempo recorded from the back swing to the down swing.