I'll explain what is meant by these questions but cannot answer them fully without examining the paper in question.

The first thing you need to know is what is reliability and validity. Reliability is basically that the data is closely grouped. This means that there is little variation in the data. Validity is a reflection of how true the data is (see the first reference for an excellent visual representation of these terms). Validity implies reliability (or consistency) but just because a data set is reliable does not make it valid. These two factors are very important in determining the meaningfulness of study results. A study may make a claim based on their results but if their data is not valid and reliable those claims are meaningless.

References:
http://www.socialresearchmethods.net/kb/rel&val.htm
http://en.wikipedia.org/wiki/Validity_%28statistics%29

The first questions asks how the researchers assessed reliability and the results they found. Reliability can be tested by replicating the experiment or by taking the measurements (in this case it would be another form of questioning the same people) using a different manner. Look to see if the researchers gave the questionnaire repeatedly to the same people to compare their results. As to what they found you will need to look at the paper in question.

Question two refers to validity and based on the information you have presented here it looks like this is the factor called into question. Validity refers to the trueness of the data. Did the researchers repeat this experiment on a control group for which they knew the data? This could be easily done in a group of elderly in a nursing home where their activity levels are monitored. Did they compare the questionnaire results with the participants' medical files? These are ways in which validity can be tested.