UK airlines receive bomb threats several times a day, every day, all year. It's absolutely routine and the vast vast majority are quickly classed as not credible by the many trained bomb threat evaluators employed 24/7 for this routine everyday task.
To shut a runway for 6 hours for a misspelled anonymous note may be perceived as disproportionate.
On a superficial level it appears at least to have the merit of being the safest thing to do. However thus ignores the risks you've now introduced. Aircraft will have to unexpectedly divert, another airport will have to cope with a sudden large increase in workload. Aircraft will be making approaches with lower reserves of fuel, pilots will be working deeper into the night getting more tired. The next day the disruption and delays to getting the aircraft back to the reopened runway will see flight duty hours reaching or exceeding normal limits. Stressed and delayed passengers will be confrontational all day.
Sure, this stuff happens and the system copes. Nevertheless shutting a runway at a major airport does drill all sorts of new holes in the Swiss cheese safety slice. It adds links to the error chain. It erodes safety margins in quite tangible ways.
It would be good if that didn't happen again
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