Any idea where "The. Sun" (a tabloid news rag) is getting its information, as opposed to what the police report says? See the report, posted once again, below. The Sun is, as usually, WRONG and just clickbait. I, for one, will appreciate knowing in advance if it's a Sun article, because I intend to ignore them, as they are entirely unreliable.
Nothing in that says that police can go inside the house unless there is probable cause. So if someone answers the door on a welfare check, and says, "Nope, everything is good here," that's the end of it. If the police say, "Well, is John Doe usually living here?" and the answer can be, "Everything is fine here, no further comment" then the welfare check was in error. You can't call in a welfare check for your neighbor's house and inquire about someone who doesn't live there. Even if the residents have a dead body in a bedroom, if they come to the door and say all is well, that's the end of the welfare check.
LE now needs to do something else to get inside - and that's called probable cause. A warrant isn't strictly needed if probable cause is strong (strong odor of decomp, house is on fire).
Police do not get to come in and look for said person. If there's no answer, they'll go round the windows most places - and in many places, they'll then get a locksmith if they have reason to believe the person is injured or dead. If. they need to break down a door, they need more authority than just a neighbor's phone call. Where I live, LE will go to nearby houses while they wait for the watch commander to weigh in and, if necessary, for a warrant (judges are on call 24/7 in my county, but that's not true everywhere).
If police were to knock doors down without warrants on the pretext of a "welfare check" (an extra-legal exercise), they can find themselves unable to use. anything they find as evidence if in fact, there is foul play. Further, people would use welfare checks to harass others (would be less illegal than Swatting, which is a misuse of 911).
Thing is, the Laundries answered the door. Welfare check over.