I can't seem to understand how tick data works. Below is some tick data for a certain security (I got this data from a platform called MetaTrader). At 09:56:28 someone offered to sell at \$9.9. But then at 09:57:40 someone offered to buy at \$12.89. Isn't that weird? If someone is selling at \$9.9 why would you offer to buy at \$12.89?
To make it weirder, at 09:57:30 the offer to sell at \$9.9 is repeated (or maybe it's someone else's offer?) even though someone was willing to buy at \$12.89. The entire dataset is like this.
Also: when people talk about the bid-ask spread do they mean that the bid and ask prices are horizontally aligned? Like at 10:06:00, when there is a bid price of \$11.27 and an ask price of \$11.28? What would the bid-ask spread be at, say, 09:59:23, when there was an ask price (\$9.43) but no bid price?