HCG (the pregnancy hormone) and LH (the hormone which peaks shortly before ovulation) are very similar to each other at a molecular level. There is something in HCG which will be recognised by an ovulation test as LH, when it is not LH. (It can also trick the human body, not just a strip test, because if you inject yourself with HCG when you have a large enough follicle, your ovaries will mistakenly think you're having an LH surge and it will trigger the final maturation stage and ovulation, which is why fertility treatment often involves HCG shots to trigger ovulation.)
But there are some important differences between HCG and LH. Firstly, any level of HCG in the blood or urine indicates pregnancy, meaning that any line on a pregnancy test, however faint, indicates pregnancy. However, there is always a certain minimum level of LH in the blood and urine even when we are not about to ovulate, which means that in order for an ovulation test to be positive, the test line needs to be darker than the control line.
For this reason, the amount of LH needed to turn an ovulation test positive is quite high (at least 100 miu, I think), whereas a pregnancy test may be positive with an HCG level as low as 5 miu.
This means that if you are pregnant, you will certainly get a line on an ovulation test, but you would anyway whether you were pregnant or not. And if you are pregnant enough to turn an ovulation test positive, you would have been testing positive on an actual pregnancy test for at least a couple of days already.
So yes, ovulation tests detect pregnancy, but they can't distinguish between LH and HCG, and they aren't a reliable method of determining whether you are pregnant or not. If you know for sure that you ovulated 2-3 weeks ago and your period is late and for some reason you absolutely can't get your hands on a pregnancy test but you have an ovulation test at home, a strong line on an ovulation test is a good sign that you probably are pregnant.